As a method to encapsulate a semiconductor device with a resin, there are transfer molding, compression molding, injection molding and the like. In the transfer molding which is more generally used, a resin composition for encapsulating a semiconductor in a tablet shape is usually supplied to a molding machine. The tablet-like resin composition for encapsulating a semiconductor can be obtained by melt-kneading an epoxy resin, a curing agent, a curing accelerator, an inorganic filler or the like using a roll, an extruder or the like, followed by cooling and pulverizing, and press-molding into a columnar or rectangular tablet (tableting). In a mass production process of the resin composition for encapsulating a semiconductor, it is continuously tableted using a unitary or rotary tablet press. At this time, however, there are failures such as breaking or cracking of tablets, or poor appearance caused by attachment of a resin composition to the inner surface of a mold in a tablet press which leads to roughness over the tablet surface, in some cases. The broken or cracked tablets cause a conveyance failure or a filling failure during a package molding process, and poor appearance causes breaking or cracking of tablets during conveyance in some cases. As a method to reduce breaking, cracking and poor appearance described above, there have been proposed, for example, a method of optimizing surface roughness of a mold in a tablet press, a method of controlling an environmental temperature or a mold temperature, and the like (for example, see Patent Documents 1, 2 and 3).
On the other hand, in the recent market trend of miniaturization, lightweightness, and high performance of electronic devices, the degree of integration of semiconductor elements has been increasing year by year, and a method for mounting semiconductor elements has been changing from an insertion mounting to a surface mounting. As the shape of the semiconductor package, there has appeared a package capable of coping with small size, light weight and high pin counts typically exemplified by a surface mounting type quad flat package (QFP), and there have further appeared a package with higher pin counts and narrower pitches of the wiring, and a package having a structure obtained by laminating chips inside one package. In such a semiconductor device, since the thickness of a resin-encapsulated portion is thin and the wire density is increased, molding failures during a package molding process, such as incomplete filling, formation of voids, wire sweep and the like, tend to easily occur, as compared to a conventional semiconductor device. Then, for the purpose of improvement of flow characteristics, there have generally been used low molecular weight or crystalline epoxy resin and curing agent for an epoxy resin and a curing agent.
However, when low molecular weight or crystalline epoxy resin and curing agent are combined, the flowability of a resin composition is improved and the molding yield rate is improved. However, breaking, cracking or poor appearance easily occurs during a tablet molding process, the tablet moldability is not fully improved in the aforementioned tableting process, and both package moldability and tablet moldability are not achieved in some cases.